If I stun an already stunned unit, does my Leona legend still give a buff to something?

Ruling: No, Leona's legend ability will not trigger because a stunned unit cannot be stunned again.

Nuances:

• A unit that is already stunned cannot be stunned a second time, so the stun effect fails to apply
• Since the stun does not successfully apply, any "when you stun" or similar triggered effects (like Leona's buff) will not activate